This invention relates in general to an overshot tool of the type having a radially expandable and contractible grapple lowerable on a pipe string about a fish stuck within a well bore to enable it to be retrieved therewith. More particularly, it relates to improvements in a tool of this type which facilitates retrieval of the fish by enabling fluid to be circulated through the pipe string and fish and then upwardly about the annulus between the string and well bore to loosen debris in which the fish is stuck, or, in the event the fish cannot be retrieved, to permit the tool to be released from the fish for recovery from the well bore.
As well known in the art, a fish is a length of pipe which, during drilling of the well bore, has become inadvertently stuck and left with the well bore as a section of the pipe above has separated therefrom. The fish must of course be retrieved or otherwise removed from the well bore in order to permit the drilling to proceed, in the event it cannot be retrieved, the tool must be removed from the well bore to permit the fish to be drilled out or otherwise removed.
For this purpose, the overshot tool of the type to which this invention relates includes a tubular body whose upper end is adapted to be connected to a pipe string for vertical movement within the well bore, a lower end which is adapted to fit over the fish when so lowered, a bowl within the body bore having helically tapered surfaces, and a seat beneath the bowl. A radially expandable and contractible grapple supported within the bowl has helically tapered outer surfaces adapted to slidably engage those of the bowl and, vertically spaced helical threads or wickers about its inner side adapted to engage the fish. More particularly, the bowl and body have aligned slots, and a packer supported on the seat has a tang for fitting within aligned slots in the body and grapple so as to limit rotation between them, whereby as the tool body is raised and rotated to the right, the grapple surfaces slide downwardly along the bowl surfaces to cause the threads to tightly grip the fish so that it may be retrieved upon lifting of the pipe string or, in the event the fish cannot be retrieved, the tool body may be jarred downwardly to release the grip of the grapple threads and thus permit the tool to be retrieved.
In accordance with one such tool, the packer assembly includes a metal body supported on the seat and having an annular groove about its bore which receives a ring of elastomeric material having a lip about its bore to engage about the fish. One problem with prior tools of this type is a tendency of the packer seal to fail or be blown out thus allowing circulating fluid to pass between the fish and inside of the tool instead of into the fish to loosen it from the debris. Thus, although some have included a seal ring including a lip intended to seal about the upper end of the fish, they tend to fail, especially in response to the high hydrostatic load of the circulating fluid above them.
For this purpose, it has been proposed to mold the seal ring into a recess within the bore of the metal body. Nevertheless, the seal often fails or is blownout so that the tool must be retrieved to permit replacement of the seal ring or replacement of the entire packer assembly if molding facilitates one not convenient. In any case, retrieval and rerunning of the tool entails considerable down time at a great expense to the operator.
An object of this invention is to provide an overshot tool of this type having a packer of such construction as to minimize these problems, in that the seal thereof is more securely carried by the packer assembly body.
Another object is to provide such a tool having alternate embodiments of the control packer especially well suited for use in recovering fish of different diameters.
These and other objects are accomplished in accordance with the novel aspects of the present invention, by a tool of the type described in which the packer assembly includes a metal body adapted to be supported on the seat and has a counterbore about the upper end of its bore and threads about the counterbore, and a ring of elastomeric materials adapted to fit closely within the counterbore of the packer body, a lip about its bore to sealably engage about the fish, and an annular recess about the upper end of its outer diameter to provide a seat on its lower end. The packer further includes a metal ring within the recess having threads thereabout adapted to be made up with the threads on the metal body to hold the elastomeric ring downwardly against the seat on the lower end of the recess.
In one embodiment of the invention, wherein the tool is adapted to fit over a relatively small diameter fish, the metal ring has an upper end adapted to terminate beneath the upper end of the metal body when made up with the metal body, and the tang is on the metal body. In another embodiment, wherein the tool is adapted to fit over a relatively large diameter fish, the metal ring has an outwardly extending flange on its upper end adapted to overhand and engage the upper end of the metal body when the metal ring is made up with the metal body, and the tang is on the metal ring. In each embodiment, the seat of the metal body has concentric ribs for biting into the lower end of the seal ring, and the metal ring has concentric ribs on its lower end for biting into the seat of the recess of the seal ring, thus more securely holding the seal ring in place.